Hi Jessip,
Upside down ? character is usually the way for Oracle db to display bad encoded character.
Is it an Oracle database?
In that case, as wodnicki told it, check the db encoding, utf8 or ISO8859P13, for instance.
Most often it comes because you inserted Win1252/ISO8859P* encoded data into utf8 character set database, or the inverted thing.
You should also check NLS_LANG/NLS_LANGUAGE if you imported data not with the Adobe Campaign worfklow collection activity, but with another ETL tool (such as SSIS, Talend, Informatica).
But if you still use Salesforce with connector and replace only Exact Target by ACC, it is a bit different, but linked to the NLS behavior.
It is the same behavior with other engines (SQL Server, MySql etc) but other displays "bad" characters instead of upside down ? sign.
The same kind of issue occurs with html templates, with copy/paste for instance declared utf8 html content but actually copied from other tool with ISO8859P*/Win1252/Mac/etc character encoding.
Regards
J-Serge